Be very direct with your friend and set boundaries. Do not use an indirect method of "re-direct away from intrusiveness, away from topics that I do not wish to follow." Tell this friend that she is not allowed to interrogate you about topics A, B, and C. If she wants the friendship to continue, she must respect your wishes. If she continues to interrogate you and violates this boundary, stand up and leave the lunch; you will know she is no friend. Good luck.